Reducing nitrogen losses from dairy farms on stony soils

In the past two decades, much dryland farming has been converted to irrigated dairy farming in New Zealand, notably in eastern areas of the South Island.   Soils there are largely shallow, free-draining, and stony.

Dairy conversions have raised concerns about increased nitrate leaching as well as adding to national greenhouse gas emissions.

What changes could be made to farm management strategies, therefore,  and how could farmers and rural decision-makers better understand how to increase soil carbon and reduce nitrogen losses from dairy farms on stony soils?

A five-year MBIE-funded collaborative research programme, Reducing nitrogen losses from farms led by Manaaki Whenua/Landcare Research’s Dr David Whitehead, set out to find out.  The research was done on-farm at Lincoln University’s Ashley Dene Research & Development Station in Canterbury.

“We aimed to provide management options to manipulate carbon inputs using different grassland and fodder species and irrigation to reduce carbon and nitrogen losses,” says Dr Whitehead.

“To understand the carbon inputs to reducing nitrogen losses, we tested whether carbon inputs to two crops could reduce the rate of nitrogen losses. Then, for measuring and modelling paddock water, carbon and nitrogen inputs and losses on stony soils, we used predictive models for irrigated and non-irrigated lucerne and tested the findings against field measurements,” explains Dr Whitehead.

Overall, researchers found the concept central to farm management practices is that increasing carbon input to the soil leads to retention of both carbon and nitrogen as soil organic matter.

“The research findings have shown that inputting of carbon to the soil is crucial to retaining nitrogen and carbon in the soil. We found soil carbon has been decreasing, and this depends on the grazing and the irrigation regime. But if we want long-term sustainability in our agricultural systems, it’s critical that we maintain increases in our soil carbon. We are also helping to mitigate climate change by removing that carbon from the atmosphere and storing it in the soil,” says Dr Whitehead.

Reducing nitrogen losses from farms was a collaboration between Manaaki Whenua, Lincoln University, Plant & Food Research, Scion, University of Canterbury and the New Zealand Agricultural Greenhouse Gas Research Centre.

The programme involved 31 research contributors, resulted in 16 scientific publications, resulted in three PhDs awarded and valuable engagement with Environment Canterbury, MPI, Overseer and Taumutu Iwi.

Source: Landcare Research

Author: Bob Edlin

Editor of AgScience Magazine and Editor of the AgScience Blog